The Simple Trick That Can Help Protect Your Outdoor Plants From Frost During Winter

Few things are more crushing to a gardener than nurturing potted and container plants all season only to lose them to a killing frost. Freezing temperatures are always a concern in the garden, but especially for vulnerable potted plants, the roots of which don't benefit from being in the cozy, insulating ground. Instead, they're above ground with greater exposure to cold air. How about a DIY preventive solution that's free, easy, and backed by science?

If you've ever huddled together with friends to try to stay warm on a cold day, you'll understand how the same kind of huddling — clustering plants together — can help protect them from frost. By pushing plants together before a frost, you are creating a microclimate that slightly raises the temperature within the cluster. Plants modify the thermal characteristics of their microclimate. The humidity produced in the cluster is one factor that protects the plants by slowing temperature change. The higher the humidity, the slower the change will be. Once you understand the science of clustering potted plants together, you may want to add this simple technique to your list of tips for protecting your plants from frost.

To cluster your potted plants, gather them together in one spot and push them closely together so pots are touching and plants benefit from each other's warmth. Place the least cold-hardy plants, along with any plants that are stressed, at the center of the cluster for extra protection. Feel free to pack as many plants as you can into the cluster. Aligning with the protective benefit of increased humidity, larger clusters of plants are more protected than smaller ones.

While the clustering technique alone might provide sufficient protection from frost in some locales, it's risky to depend only on grouping your plants together. Two additional measures will greatly enhance the effectiveness of clustering. First, place your cluster against a sheltering area, such as an exterior wall of the house or garage. These are "thermal mass" elements that store heat. Plants benefit when this heat is released. Structures can also protect against wind and snowstorm damage.

The second way to supplement the clustering technique is to cover your clustered plants with mulch for extra insulation to help plants retain heat. Mulching will also help protect plant roots. Some gardeners take even more measures, such as wrapping pots in burlap or bubble wrap and covering plants with sheets or similar materials (see our guide to how to cover plants from frost). Consider trying the clustering technique in a protected area, along with mulching, and be sure you're aware of garden hacks that won't actually protect your plants from frost.